More than just being a fun, unique game, there are two really obvious reasons "Fortnite" has become dominant:

It's free!

More importantly, it doesn't feel free — it presents as a polished, premium game that could stand up to blockbusters that cost upwards of $60.

"Fortnite" is part of an emerging category of games that offer a premium experience with zero upfront cost. The game is, of course, making money otherwise — somewhere in the ballpark of $225 million in March alone, according to the analytics firm Superdata.

Here's how an unknown game with a unique premise rocketed from obscurity to stardom without charging a dime.

Being good at a game and helping fans learn how to get better is a theme among Twitch streamers, but Blevins has captured the zeitgeist with his streams. Since anyone can play the game — and because it's relatively easy to learn the basics (third-person shooting) — more than 40 million people have already jumped in.

And where do those people look when they want to improve? They look to Blevins.

He's making somewhere in the realm of $500,000 monthly playing "Fortnite" on his Twitch streams. And that's before we talk about the many other revenue streams Blevins operates.

He's making all that money from being really good at "Fortnite," a direct translation of his longtime skills as a professional gamer. One main reason people watch Blevins is because he teaches them how to be better at "Fortnite."

"Fortnite" doesn't feel like a free game.

It's difficult to put a finger on exactly what it is, but there's a subtle difference between most paid games and most free-to-play games.

Part of it is expectation. If someone pays $60 for a game, they expect a polished, immersive, expansive experience. On the flipside, paying nothing for a game lowers the stakes dramatically. If it's bad, the only thing you've wasted is your time.

In the case of "Fortnite," it doesn't feel as vacuous as so many free-to-play games. There are no timers stopping you from doing certain things accessible only by paying to speed them up or waiting for hours in real time. Quite the contrary — "Fortnite" feels like a premium experience.

There's a good reason for that. "Fortnite" was in development for years, designed as a tower-defense game (now known as the "Save the World" mode). The free mode everyone is playing, "Fortnite: Battle Royale," was built on top of a highly polished game.

It feels like a premium game because it basically is a premium game.

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"Fortnite" is on everything.

Epic Games

Own a PlayStation 4, or an Xbox One, or a PC, or a Mac, or an iPhone/iPad?

If you answered yes to any of those, you're able to play "Fortnite." And that accessibility is huge for growing player numbers. If you're even remotely interested in playing "Fortnite," chances are you can, today.

Maybe your friend is playing on an iPhone, and you like playing on another platform? You can probably play together! The game allows players on various platforms to do so, except for Xbox One-PlayStation 4.

It's free, and it's everywhere — making it really easy to say yes to playing "Fortnite" if you've never tried it. And that's huge.

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So how does "Fortnite" make so much money if it costs nothing? Simple: by selling stuff.

"Fortnite" makes money by selling its Battle Pass and various in-game cosmetic items.
Epic Games

You could download "Fortnite: Battle Royale" today on your PlayStation 4, Xbox One, PC, Mac, or iPhone/iPad. It costs nothing to download and play. And you could never pay a cent for the game.

Pretty sweet!

Alternatively, you could become one of the tens of millions of people obsessed with the daily/weekly/monthly/seasonal grind of the game's "Battle Pass," a system for leveling up your character and unlocking items.

In a brilliant move, you can play "Fortnite" for free in perpetuity — but if you want to unlock sweet, sweet loot, you have to pay for the game's Battle Pass.

More simply: Playing "Fortnite" is free, but progressing through the game's loot-unlock system is not.

You can outright purchase in-game currency ("V-bucks") and use it to buy in-game stuff. But none of that stuff offers an advantage over other players — it's strictly cosmetic. Maybe you want an outfit for your character, or a new dance move, or a different-looking pickax.

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BONUS: There's one other major reason that "Fortnite" has blown up even more than its main competitor, "PlayerUnknown's Battlegrounds." Can you guess what it is?

PUBG Corp. and Epic Games

"Fortnite" and "PlayerUnknown's Battlegrounds" are the same type of game, known as battle royale.

These are shooters that pit 100 players against one another in a winner-take-all match to the death. And on paper, they're very similar games.

In reality, the differences are stark, and the most obvious is entirely visual.

"Fortnite" is a cartoony, visually pleasing game. You might be blasting people with shotguns and assault rifles, but it feels, at worst, as if you're shooting paintball guns. When another player "kills" you, there's no blood — you just disappear from the world as the game transitions to following whoever took you out.

On the contrary, "PUBG" is visually dreary and serious and ... distinctly less fun as a result.

It's a subtle difference — one of several that distinguish between the two games — but it makes a big difference in reality.

I'm far more inclined to spend time in the silly, colorful world of "Fortnite" than the post-apocalyptic sadness of "PUBG." And I doubt I'm alone in that feeling.